Why doesn't ORDER BY 'id' 'desc' return a syntax error?

Question

I was testing some apparently wrong code and was quite sure it should return a syntax error. But it didn't. The following query works without errors (albeit doesn't sort the table either, which at least meets my expectations):

SELECT * FROM dummy ORDER BY 'id' 'desc';

Interestingly, that

SELECT * FROM dummy ORDER BY id 'desc';

does produce a syntax error.

How does MySQL interpret two strings after ORDER BY? What does it take these strings for? Here is the MCVE